It's understandable to be confused about exactly what sort of protection you'll get from a COVID-19 vaccine.
Key points:
Data from the UK shows both AstraZenecca and Pfizer vaccines stop about 80pc of infections
A person who becomes infected after being vaccinated is half as likely to pass the virus on to the people they lived with
The Pfizer vaccine is known to be 97pc effective at keeping infected people out of hospital
Plenty of people have contacted the ABC with questions – how come we're hearing about vaccinated people getting COVID? Won't a vaccine stop me getting it? If I'm vaccinated, can I still give it to my family? And if I'm vaccinated and I do get COVID, just how sick will I get?
What can be confusing is that the vaccines do lots of things and aren't perfect.
And to make it more confusing, vaccines work in a certain way when most of the population get them – but that's different to how they work if only some people get them.
Let's break it down.
Do vaccines stop me getting COVID-19?
Firstly, being vaccinated with either of the shots available in Australia gives you very strong protection against being infected with COVID-19.
We know that in countries with high vaccination rates, both the Pfizer and AstraZeneca jabs have stopped enormous numbers of people getting infected.
When the vaccines were first approved, trials showed the AstraZeneca vaccine stopped about 70 per cent of infections, and Pfizer 90 per cent.
Now that we've been able to study how effective the vaccines are when given to a broad range of people in the community, there doesn't seem to be any significant difference between the two. Preliminary data from the UK suggests they both stop about 80 per cent of infections.
But no vaccine is able to protect everyone all the time. When there is a lot of virus around, some vaccinated people will still get infected, but in most cases vaccinated people experience mild symptoms – we'll come back to that later.
Unsplash
)To get the full benefit of the COVID vaccines, people need two doses. And even then, it takes a couple of weeks for your immune system to fully kick into gear.
Vaccine expert Kylie Quinn from RMIT says the reason vaccines are not 100 per cent effective is that people have different immune systems, so some people get a strong response to the vaccine, where others have a weaker response.
"Some of that is because of their biology and their health and some of that's just luck of the draw," she said.
It's a bit like wearing a seatbelt: It won't always stop you being injured, but you are much more likely to be OK after an accident if you are wearing one."
Dr Quinn said you are clearly better off having the shot even though some vaccinated people will still get infected.
"The vaccine just makes the chances of that much rarer."
There are reports of vaccinated people getting the Delta strain. What's that about?
You may feel like you are hearing about vaccinated people contracting the Delta strain of COVID-19 more than you did with other strains.
That is partly because the Delta strain is better at infecting everyone.
It spreads more easily and faster among people, so more people are becoming infected with the Delta strain on the whole.
Some studies show a person who has the Delta strain will produce more than 1,000 times as many viral particles as a person infected by other strains – and that means anyone in contact with the person infected with the Delta strain is more likely to be exposed to the virus.
That's why, vaccinated or not, we're all more likely to contract the Delta strain of COVID-19 than earlier variants.
ABC News: Eliza Laschon
)The current Sydney outbreak gives us an insight into how contagious the Delta strain can be. For example, out of 50 people who breached restrictions to farewell a loved one, 45 have now tested positive and one person has died.
The Delta strain also appears to be better at dodging our immune response, which means vaccines may not give us the same amount of protection against the Delta strain and any immunity we might get after being infected with other strains might be reduced.
Even so, data from the UK shows the vaccines remain very effective against Delta.
Can I pass it on to others if I'm vaccinated?
If you do get the virus after you're vaccinated, you can still pass it on but, given you are less likely to become infected in the first place, you will be less of a risk to those around you.
Evidence from earlier this year showed a vaccinated person was less likely to infect others, but Delta might be changing that.
When a person is suffering from COVID-19, the coronavirus is reproducing inside their cells and being expelled when they sneeze, cough, talk and breathe.
ABC Goulburn Murray: Charmayne Allison
)We know infected people who produce large amounts of the coronavirus are more likely to pass the disease on and studies in Israel and the UK have shown a vaccinated person who contracts COVID-19 produces and expels far fewer viral particles.
Another study of how COVID-19 spread through more than 365,000 households in England showed that if a person became infected after being vaccinated, they were half as likely to pass the virus on to the people they lived with.
But that was before Delta became the dominant strain, so Australian health authorities will be looking to evidence of how that variant behaves because that’s the strain we are currently dealing with.
Unfortunately, the Centres for Disease Control in the US now thinks people who get infected with the Delta strain after vaccination might spread the virus just as easily as people who haven't been vaccinated.
Their study still clearly shows vaccines offer significant protection, even though they don’t prevent infections entirely.
What are my chances of severe disease or landing in hospital if I'm vaccinated?
Now that millions of people have been vaccinated across the globe, we can see that two full doses of either the Pfizer or AstraZeneca vaccine are extremely effective at keeping people out of hospital.
Australia has had extremely low rates of vaccinated people testing positive for COVID-19 and needing to be treated in hospital. Between March and July, 610 people in NSW tested positive for COVID-19 and only 10 of them had been fully vaccinated.
AAP: Aaron Bunch
)By global standards, we have also had very low rates of positive cases – and low rates of vaccination — so we can get a better read looking overseas.
In the US, 97 per cent of people hospitalised with COVID-19 are unvaccinated.
Data from Israel showed the Pfizer vaccine was 97 per cent effective at keeping infected people out of hospital, while another study from Britain showed AstraZeneca was 92 per cent effective and Pfizer 95 per cent effective at preventing hospitalisation after infection with the Delta strain.
Dr Quinn said making sure people are not getting severely ill and being hospitalised is what vaccines are all about.
"Even with the most challenging version of the virus, this is the most important outcome that we want to measure," she said.
Can I die if I'm fully vaccinated?
In the UK, where the Delta strain has been dominating, vaccination with either AstraZeneca or Pfizer has stopped about 80 per cent of infections altogether, and is 95 per cent effective against symptoms.
If you don't get symptoms then the infection you've got isn't bad and you won't wind up in hospital or die.
But around the world, some people who have died have been fully vaccinated. Earlier we explained that vaccines have prevented a lot of deaths – but also that they're not perfect. So while they haven't prevented every death in the vaccinated population, vaccines are the best thing we've got to avoid fatalities.
Can vaccinated people do things unvaccinated people should not?
We all want to get back to a life in which masks are not mandatory, restaurants and bars are open and overseas travel is possible.
But just because you are vaccinated does not mean public health orders are not for you.
As mentioned above, if you are unlucky enough to get the Delta strain after being vaccinated, it's possible you'll be able to pass the virus on just as easily as someone who has never been infected. So it's a tricky issue.
The key to getting life back to normal is getting so many people vaccinated the virus isn't able to spread effectively, known as achieving "herd immunity".
Until then, we may have to get used to restrictions coming and going.
ABC News: Michael Clements
)Overseas, authorities have tried to give vaccinated people more freedom and it hasn't always gone well.
Two months ago in the US, the Centers for Disease Control and Prevention said only unvaccinated people needed to wear masks. It's since done a backflip and now says vaccinated people should wear masks indoor in parts of the country where the virus is surging.
In late June, authorities in the Netherlands wound back restrictions and swung open nightclubs and festivals, allowing in anyone who was vaccinated. They then had to slam things shut again when infection rates soared by 500 per cent.
Once our vaccination rates are higher, we will inevitably start to relax certain restrictions. In NSW, Premier Gladys Berejiklian has said once 80 per cent of the adult population is vaccinated, lockdowns won't need to be so severe.
But Dr Quinn said there's one thing that needs to happen before that's possible.
"The first thing you have to do, though, is to make the vaccine accessible to folks," she said.
"We need to ensure that people have had a reasonable chance to access the vaccine, had the chance to get vaccinated, before we start introducing mechanisms like that."
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